Agents which block the formation of second messengers which mediate growth factor action may be of value in cancer chemotherapy. We have developed test systems to identify drugs which interfere with phosphatidylinositol formation or hydrolysis, because the formation of inositol phosphates has been implicated in the action of a number of growth factors including platelet derived growth factor and bombesin. A series of rationally-designed inhibitors of enzymes involved in phosphatidylinositol metabolism are currently being synthesized for evaluation